Electric motor control

ABSTRACT

A method and apparatus is disclosed for controlling a system comprising at least one electric motor. The system includes aspects which permit, among other things, electromagnetically disconnecting a failed permanent magnet motor from said system, weight savings in motor control electronics, controllability benefits and other benefits.

TECHNICAL FIELD

The invention relates generally to electric motors and, moreparticularly, to the control of electric motors.

BACKGROUND

Motors, such as permanent magnet motors, may be controlled in a varietyof ways, but the control electronics can often be heavy and lackcompactness. Also, the control of multiple electric motors connected todrive one load typically requires a mechanical disconnect system todisconnect a failed motor from the load, since the failed motor maybegin to operate as a generator, potentially creating drag torque andinternal heating of the motor. Accordingly, there is a need to provideimprovements which address these and other limitations of prior artmotor control systems.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an electric motor systemcomprising a motor having a magnetic rotor and a magnetically conductivestator, the stator having at least two windings connected with oneanother in series, the rotor and stator together defining at least afirst magnetic circuit encircling a first portion of a first one of thestator windings, the stator defining at least a second magnetic circuittherein, a second one of the stator windings wrapped around a portion ofthe stator remote from the first magnetic circuit, the second statorwinding and said portion of the stator thereby providing an inductorassembly, the second magnetic circuit passing through said statorportion and encircling a second portion of the first stator winding anda portion of the second stator winding, the second magnetic circuitremote from the first magnetic circuit and remote from the rotor, themotor system having a buck regulation apparatus connected in seriesbetween a direct current (DC) electricity source and the second winding,wherein the inductor assembly provides a filter inductor function forthe buck regulator.

In another aspect, the present invention provides a method forcontrolling an electric motor system, the system including at least onemotor having a magnetic rotor and a magnetically conductive statorhaving at least one winding, the rotor and stator together defining atleast a first magnetic circuit encircling a first portion of a first oneof the stator windings, the stator defining at least a second magneticcircuit therein, the second magnetic circuit encircling a second portionof the first stator winding, the second magnetic circuit remote from thefirst magnetic circuit and remote from the rotor, the method comprisingthe steps of operating the motor to drive an output shaft thereof, thestep of operating including the step of saturating at least a portion ofthe second magnetic circuit to maintain an impedance of said winding ata first, value during operation, detecting a fault in the motorrequiring motor shutdown, and then shutting down the motor, includingthe step of de-saturating at least said portion of the second magneticcircuit to increase the impedance of the winding to a second value, thesecond value significantly higher than the first value such that currentflow in the winding is effectively limited to a desired value.

Further details of these and other aspects will he apparent from thedetailed description and Figures included below.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying Figures in which:

FIG. 1 is a cross-section of a permanent magnet motor;

FIG. 2 is a partial schematic of the motor of FIG. 1;

FIG. 3 is a isometric view of a portion of a phase winding of the motorof FIG. 1;

FIG. 4 is a schematic of an arrangement of two motors according to FIG.1;

FIG. 5 is a schematic diagram of a control, scheme arrangement for themotors of FIG. 1 and/or 4;

FIG. 6 is a cross-sectional view, similar to FIG. 1, of a anotherarrangement for a motor; and

FIG. 7 is a schematic diagram of a control scheme for the motor of FIG.6.

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2, a permanent magnet (PM) electricmachine 10 is depicted. For ease of illustration and description, FIG. 2shows a linear arrangement of the electric machine 10 of FIG. 1.However, it is to be understood that the machine 10 is generallypreferred to have the circular architecture of FIG. 1, with an inside oroutside rotor (FIG. 1 shows an inside rotor, which is preferred but notrequired). It will also be understood by the skilled reader that theFigures, as well as the accompanying description, are schematic innature, and that routine details of machine design, have been omittedfor clarity, as will be apparent to the skilled reader. The machine 10may be configured as an alternator to generate electrical power, a motorto convert electrical power into mechanical torque, or both. The motoraspects of such a machine are primarily of interest in the followingdescription, and hence machine 10 will now be referred to as motor 10.

The motor 10 has a rotor 12 with permanent magnets 14, interposed byspacers 16, which rotor 12 is mounted for rotation relative to a stator20. A retention sleeve (not shown) is typically provided to hold thepermanent magnets 14 and the spacers 16. Stator 20 has at least onephase winding 22 and preferably at least one control, winding 24 (bothwindings are represented schematically in the Figures as a solidrectangles in cross-section, but the skilled reader will appreciate eachmay comprise multiple turns of a conductor, as described below). In theillustrated embodiment, the stator 20 has a 3-phase design with threeessentially electromagnetically-independent phase windings 22 (thephases are denoted by the circled numerals 1, 2, 3, respectively in FIG.2) and, correspondingly, three control windings 24. The phase windings22 and control windings 24 are separated in this embodiment by a windingair gap 26 and are disposed in radial slots 28, divided into slotportions 28 a and 28 b, provided in the stator 20 between adjacent teeth30. For ease of description, the adjacent slots 23 a, 28 b are indicatedin FIG. 2 as A, B, C, D, etc. The phase windings 22 are electricallyinsulated from the control windings 24. A back iron 32, also referred toas the control flux bus 32 in this application, extends between and atthe bottom of the slots 28 b. A rotor air gap 34 separates rotor 12 andstator 20 in a typical fashion. A core or “bridge” portion, alsoreferred to as the “power flux bus” 36 portion of stator 20 extendsbetween adjacent pairs of teeth 30 in slot 28 to form the two distinctslots 23 a and 28 b. The first slots 28 a hold the phase windings 22only, and the second slots 28 b hold both the phase windings 22 andcontrol windings 24.

The materials for the PM motor 10 may be any one deemed suitable by thedesigner. Materials preferred by the inventor are samarium cobaltpermanent magnets, copper phase and control windings, a suitableelectromagnetic material(s) for the stator teeth and power and controlflux buses, such, as electrical silicon steels commonly used in theconstruction of electromagnetic machines. The stator teeth, power andcontrol flux buses may be integral or non-integral with one another, asdesired. Each of the phase windings 22 in this embodiment consists of aconductor with turns per slot, which enters, for instance, the firstslot portion 28 a of a selected slot 28 (e.g. at slot “A”), extendsthrough the slot and exits the opposite end of the slot, and thenradially crosses the power flux bus 36 to enter the second slot portion28 b of the same slot 28 (e.g. at slot “A”), after which it extends backthrough the length of the selected slot, to exit the second slot portion28 b, and hence exits the slot 28 on the same axial side of the statoras it entered. This path is repeated times to provide the 4 turns of thephase winding in that slot set 28 a, 28 b, before proceeding to the nextrelevant slot set in the stator. The conductor of phase winding 22 thenproceeds to the second slot 28 b of the next selected slot 28 (e.g. slot“D” in FIG. 2), where the phase winding 22 then enters and passes alongthe slot 28, exits and radially crosses the power flux bus 36, and thenenters the adjacent first slot portion 28 a of the selected slot 28, andthen travels through the slot again to exit slot 28 a and the statoradjacent where the winding entered the slot 28 b of the selected slot28. This path is also repeated times to provide the turns of the phasewinding in this slot set 28 a, 28 b, before proceeding to the nextrelevant slot set in the stator. The phase winding then proceeds to thenext selected slot 28 (e.g. slot “G”), and so the pattern repeats forsecond phase winding 22 corresponding to phase 2 (not shown), begins inan appropriate selected slot (e.g. slot B of FIG. 2) and follow ananalogous path, but is preferably wound in an opposite winding directionrelative to winding 22 of phase 1. That is, the phase 2 winding 22 wouldenter the selected slot (slot B) via slot portion 28 b (since phase 1winding 22 entered slot A via slot portion 28 a, above), and thenfollows a similar hut opposite path to the conductor of phase 1, fromslot to slot (e.g. slots B, E, etc.). Similarly, the phase 3 winding 22is preferably oppositely-wound relative to phase 2, and thus enters theselected slot (e.g. slot “C”) of the stator via slot portion 23 a, andfollows the same general pattern as phase 1, but opposite to the patternof phase 2, from slot to slot (e.g. slots C, F, etc.). Thus, asmentioned, the phases of the phase winding 22 are oppositely-woundrelative to one

another, for reasons described further below. FIG. 3 shows an isometricfree-space view of a portion of a phase winding 22 wound, as just,described, but for the fact that only two turns are shown for reasons ofdrawing clarity.

Meanwhile, a control winding (s) 24 is wrapped around the control fluxbus 32, in a manner as will now be described. In this embodiment,control winding 24 preferably forms loops wrapped preferably in apositive turns ratio relative to the phase winding. In this case, acontrol-to-phase turns ratio of 3:2 is preferred, such that the controlwinding is wrapped 6 times around the control flux bus 32 (relative tothe phase winding's 4 turns), for reasons described below. The controlwinding 24 and control flux bus 32 thus provide an integral saturableinductor in stator 20, as will be discussed below. The direction ofwinding between adjacent second slots 28 b is preferably the same fromslot to slot, and thus alternatingly opposite relative to the phasewinding 22 of a same phase wound as described above, so that asubstantially net-zero voltage is induced in each control winding 24, aswill also be described further below. Preferably, all loops around thecontrol flux bus 32 are in the same direction. Note that the controlwinding 24 does not necessarily need to be segregated into phases alongwith the phase windings, but rather may simply proceed adjacently fromslot to slot (e.g. slots A, B, C, D, etc.). Although it is preferred toalternate winding direction of the phase windings, and not alternatedirection of the control windings, the phase and control windings arepreferably wound in relative opposite directions and in equal slotnumbers to ensure a substantially net-zero voltage is induced in eachcontrol winding 24 as a result of current flow in the phase windings 22,so that the function described below is achieved. If the control windingis segregated into phase correspondence with phase windings 22, forexample to reduce its inductance by a series parallel arrangement,preferably there are equal numbers of slots of a given phase in whichthe phase winding and control winding are wound in opposite directions,to yield the desired induced net-zero voltage.

In use, in a motor mode, a 3-phase power source drives phase windings22, which result in current flow in phase windings 22 and a primarymagnetic flux along magnetic flux path or magnetic circuit 60.Interaction of permanent magnets 14 and primary magnetic flux causesrotor 12 to move relative to stator 20. When the current flow in phasewindings 22 is appropriately controlled, the motor 10 rotates with aspeed and torque. A current or voltage controller appropriately controlsthe current flow to the phase windings 22 such that an appropriate speedand torque is obtained. The current in the control windings in normaloperation of the motor is substantially the same as the current flow inthe phase windings, because they are connected in series, except that inthis embodiment current is preferably DC in the control windings, and ACin the phase windings. The implications for motor control will bediscussed further below.

Primary magnetic circuit 60 includes rotor 12, magnets 14, rotor air gap34, power flux bus 36 and the portion of stator teeth 30 between rotor12 and power flux bus 36. Primary magnetic circuit 60 encircles aportion of phase winding 22 and is generated in motor 10 by the combinedeffect, of the rotor magnets and an electrical current in phase windings22. Secondary magnetic circuit 62 includes power flux bus 36, controlbus 32 and the portion of stator teeth 30 between control bus 32 andpower flux bus 36. In this embodiment, secondary magnetic circuitencircles the portions of the phase winding 22 and control winding 24 inslot 28 b. Power flux bus 36 divides slot 28 into two slot portions oropenings 28 a and 28 b, with one opening 28 a for the phase windingonly, and another opening 28 b for the phase and control windings. Theprimary magnetic circuit encircles an opening 28 a while the secondarymagnetic circuit encircles an opening 28 b. Opening 28 a is preferablyradially closer to the rotor than opening 28 b. Power flux bus 36 iscommon to both the primary and secondary AC magnetic circuit paths inthis embodiment. AC current in the phase windings 22 causes a secondarymagnetic flux to circulate secondary magnetic circuit 62 when thecontrol bus 64 is not in a saturated state. The primary and secondarymagnetic circuits are non-overlapping (i.e. non-intersecting), andremote or isolated from one another. The second magnetic circuit isremote from, and does not include, the rotor and is preferably definedwholly within the stator assembly.

A tertiary magnetic circuit 64 preferably circulates around control bus32, as partially indicated in FIG. 2 (i.e. only a portion of thetertiary circuit is shown, as in this embodiment the tertiary circuitcirculates around the entire stator 20). The control flux bus 32 ispreferably common to both the secondary and tertiary magnetic circuitpaths and thus the secondary and tertiary magnetic circuits are snare acommon portion, namely the control bus 32, as will, be discussed furtherbelow. At least a portion of control flux, bus 32 is saturable by theflux density of the tertiary magnetic circuit.

Magnetic flux preferably circulates the tertiary magnetic circuit 64 inthe same direction around the control flux bus 32. As mentioned above,although the control winding 24 is provided in the second slots 28 bcorresponding to a particular phase of the three-phase machinedescribed, the phase windings 22 are wound in the opposite direction ineach first slot 28 a which is due to the opposite polar arrangement ofthe magnets 14 associated with each adjacent first slot 28 a of thephase. To ensure that a uniform direction for the tertiary magneticcircuit 64 is provided, as mentioned, the control windings 24 arepreferably wound in the same direction in ail second slots 28 b.

When the control flux bus is magnetically saturated, the inductance(thus impedance) of the phase windings is very low, as if there where nosecondary AC magnetic circuit. However, if zero current is applied tothe control winding (i.e. the control winding is open circuited, orotherwise switched off), the impedance of the phase windings increasessignificantly, thus limiting the current that can flow in the phasewindings, which may be used to remediate, for example, a faultedcondition, such as an internally shorted phase winding or short circuitsin the drive electronics. This impedance control has beneficialimplications for PM motor control, discussed further below.

It is to be understood that the above description applies only to phase“1” of the described embodiment, and that similar interactions, etc.occur in respect of the other phases. Further details and aspects of thedesign and operation of motor 10 are found in applicant's co-pendingapplication Ser. No. 10/996,411, filed Nov. 26, 2004, the contents ofwhich is incorporated herein by reference.

Thus, in use, in a motoring mode, a power source drives phase windings22, and control windings 24. Since in one particular arrangementdepicted in FIG. 5 the two are effectively connected in series, thecontrol winding current is equivalent, (i.e. in magnitude) to the phasewinding current. As a result of the 3:2 turns ratio between these twowindings, the slightly higher number of turns in the control windinghelps ensure that the control bus is always in a fairly saturatedcondition during normal motor operation, so as to enable efficientfunctioning of the motor at any drive current. As discussed above,although the AC flux in the phase windings tends to cancel out the DCflux in the control winding in the control bus sections where the fluxdirections are in opposition, the 3:2 turns ratio bias in the controlcoil, prevents the fluxes from actually cancelling. Thus, when thecontrol flux bus 32 is magnetically saturated by the action of currentflowing through the control winding 24, the inductance (thus impedance)of the phase windings 22 is very low, as if there where no secondary ACmagnetic circuit, and hence the control windings and secondary magneticcircuit would be essentially “invisible” to the motor during normalmotor operation.

In the arrangement depicted in FIG. 5 the number of turns on the controlwinding slots will typically be chosen to be more than the number ofturns in the phase winding slots, such to ensure saturation of thecontrol bus (however preferably not much into saturation, since someinductance in the control winding is a useful, inductor for the buckregulator filter function as described below) by having a preferablyjust marginally more ampere turns on the control winding than on thephase windings in the secondary magnetic circuit. The DC flux in thecontrol bus typically dominates relative to the opposing AC flux densityin the secondary magnetic circuit, holding the control bus in saturationdown to quite low relative values of drive current provided, via thecontrol winding to the phase windings, even under the effects of thecounter fluxes from the phase windings (i.e. the portion of the phasewinding carrying AC in the negative portion of the cycle tends to reducesaturation of the control flux bus, unless the control ampere turns arehigh enough to maintain saturation).

In use in a fault or shut-down mode, when the drive current to the motoris at or close to zero, i.e. such as when, the motor is shut down inresponse to a fault condition, the control bus de-saturates (as a resultof no control current being supplied) and, as a result, the interactionbetween the primary and secondary magnetic circuits and theinductor-like effect of the control winding 24, impedes any significantgenerated currents from flowing in the phase windings due to continuedrotation of the shut-down motor and any short circuit failure in themain phase circuits. Further discussion is found in applicant'sco-pending application Ser. No. 10/996,311.

FIG. 4 shows a redundancy arrangement in which two motors 10 areco-mounted on the same output shaft 66, and driven by suitable motordrives 68, each in communication with a system controller 69, andoperated as described above. If one motor 10 should fail in a shortcircuit, open circuit or ground (whether in the motor itself or thedrive electronics or lead wires), the drive(s) 68 preferably adjustscontrol of the remaining motor 10 (or motors 10, if there are more thantwo provided in total, and two or more are to remain operational in theevent of the shutdown of one) to compensate for the resulting loss intorque, and the failed motor is no longer driven. The controller 69provides the appropriate control to motor drives 68. As described above,the failed motor is also in effect disconnected, by bringing currentflow in its windings to zero, resulting in the impedance of the mainphase windings of the failed motor increasing to a high value, aspreviously described, such that the drag torque due to a short circuittype failure is minimised. Motor failure detection 84 may be achievedusing any suitable approach, such as incorrect speed or torque as afunction of current, voltage, high temperature, machine impedance, etc.Failure detection preferably results in a signal provided to anappropriate controller for interrupting the current supply to the motorsystem (i.e. bringing current flow to zero, as mentioned above).

FIG. 5 shows a simplified example control scheme for a motor drive 68for driving a motor 10. It should be noted that the motor 10schematically depicted in FIG. 5 depicts only a single control windingfor the 3 phases of its associated phase winding set, the controlwinding proceeding slot-to-slot in the stator irrespective of the phasearrangements of the phase windings. As discussed generally above, thisis just one of many control winding arrangements possible, and theskilled reader will be able to apply the present teachings to sucharrangements in light of the teachings herein.

The motor 10 is driven by a motor drive 68, preferably comprising a3-phase H-bridge commutation circuit 70 driving the phase windings 22 ofthe motor 10. The commutation scheme is preferably a six step 120-degreeoverlapping scheme in a “drake before break” sequence. This sequence inconjunction with a feedback diode 73 reduces high amplitude voltagespikes occurring at the input of the inverter section of the H-bridgecommutation circuit 70 due to the inductive effect of the controlwinding 24 of motor 10. Current flow to the motor, and thus the motor'storque and speed, is adjusted using a suitable pulse width modulatedsupply system or “buck regulator” circuit 72 connected to controlwinding 24 of the motor 10. The buck regulator may be any suitablecircuit. The skilled reader will appreciate that buck regulatorstypically require a filter inductor as an energy storage device forstepping down the voltage level. In this configuration, the buckregulator 72 uses the control winding(s) 24 as its inductor, thuseliminating the need for an additional inductor, and consequentlyreducing the weight of the buck regulator 72. This filter inductorreplacement role of the control winding may dictate design features ofthe control winding, as the designer will consider the buck regulatorrequirements as well as the motor requirements in providing a suitablecontrol winding configuration. The output of the control winding 24 isconnected to the inverter section of the H-bridge commutation circuits70, such that a DC-current in the control winding 24 becomes AC currentto the phase windings 22 of the motor 10.

A feedback 82 of the drive current level is provided to a buck regulatorcontroller 74 using a current sensor 76. The buck regulator andcontroller are of any suitable type, which includes suitable typeswell-known to the skilled reader, and thus need not be discussed furtherhere.

In use, the buck regulator 72 varies the current flow to the phasewindings 22 of the motor 10, and thus controls the torque and speed ofthe motor 10, based on an input torque/speed request 78 received fromsystem controller 69. Current is provided from a DC source 80 to thephase windings 22, via the control winding 24, as already described.

Referring again to FIG. 4, preferably both motors 10 and theirassociated controllers 68 are arranged as described with reference toFIG. 5, to provide a dual-redundant motor system. To enhance redundancyprotection, preferably separate DC sources 80 are provided for eachmotor system. The operation of such a dual redundant system according toFIGS. 1-5 will now be described.

Referring again to FIGS. 4 and 5, in a normal operation mode of themotors 10, the drive 68 to each motor 10 is adjusted so that the motorscontribute in desired proportions to the torque delivered to shaft 66,and the shaft rotates at a desired speed, as requested by systemcontroller 69. Both motors 10 are preferably driven concurrently toprovide torque and, when a higher efficiency operation or higher poweroperation is desired, the respective drives 68 can be adjustedaccordingly to adjust the contribution proportion of each motor 10. Thecontrol winding 24 of each motor 10 functions as the filter inductor forits respective buck regulation circuit, as described above. Also asdescribed above, the control winding 24 of each motor preferably alsokeeps its respective control bus saturated (by virtue of the relativeturns ratio between phase and control winding) to keep the controlwinding otherwise virtually “invisible” to the motor 10. Should onemotor 10 fail, such as in a short circuit, open circuit or ground, thedrive 68 to the other motor 10 can be adjusted using its buck regulator72 to increase the AC input to the phase windings 22 of the operationalmotor 10 to compensate for the loss in torque caused by loss of theother motor 10. As the skilled reader will appreciate, the failed PMmotor 10 can tend to add drag and heat to the system, however with thepresent arrangement the failed motor 10, can be “turned off” by nolonger energising the windings (i.e. and thus the current in the controlwinding is reduced to zero), which thus adjusts the failed motor 10 to ahigh impedance condition for the phase windings, as already described,thereby minimising drag and heat generation. The currents to therespective control windings and inverters is controlled by externalcontrol signals provided to the buck regulator circuits. If the systemcontroller 69 requests zero current, then the relevant buck regulatorstops providing current accordingly. This control command is preferablybased on the system, controller 69 detecting a fault or other command toset the current to sera. The resulting adjustment of the impedancecharacteristics of the phase windings of the affected motor 10, from lowimpedance during proper motor function to a high impedance in the failedcondition, results in much improved operation and controllability,particularly in PM motors where rotor excitation cannot be independentlycontrolled.

FIG. 6 illustrates a 3-phase, “dual channel” m motor 10* according tothe general “multi-channel” principles described in applicant's U.S.Pat. No. 6,965,133, but modified in accordance with the above teachings,as will now be discussed further. The same reference numerals are usedto denote the analogous elements described with reference to theembodiments above, and thus all elements will not be redundantlydescribed here. Stator 20 of dual channel FM machine 10′ is conceptuallydivided into an “A” half and a “B” half, thus providing a distinctstator sector for each channel, each channel provided with its ownindependent windings sets. Thus windings 22 and 24 will be described interms of phase winding sets 22A and 22B and control winding sets 24A and24B, as discussed further below. Other features associated with channelsa and B are also described as “A” or “B”, specifically, to indicatetheir respective channels,

Motor 10′ has a multi-channel architecture (in this case, dual channel),in that a plurality of circumferentially distributed distinct and fullyindependent (i.e. electromagnetically separate) “sets” of phase andcontrol windings are provided in each stator sector corresponding to themultiple channels. In this case, two such sets of 3-phase phase andcontrol windings are provided, namely a 3-phase set of phase windings22A and 22B and respective control windings 24A and 24B (which happen tobe single phase in this embodiment). This multi-channel architectureprovides a plurality of functional “motor elements” within the samemachine structure, which may either be operated in conjunction, orindependently, as desired. The construction of motor 10′ is otherwisegenerally as described above with respect to the single channelembodiment of motor 10.

The dual channel FM motor 10′ provides a single rotor rotating relativeto two effectively independent stators, or stator sections. Thus, rotor12 rotates relative to a stator sector 20A (i.e. the portion of stator20 with phase windings 22A) and also relative to a stator sector 20B(i.e. the portion of stator 20 with phase windings 22B). When operatedas a motor, the two “motors” (i.e., in effect, motors 10′A and 10′B) aredriven independently, as described generally above with respect to motor10, but are synchronized such that they co-operate, as if only one“motor” is present. In normal motoring mode, the two “motors” (10′A and10′B) of motor 10′ are operated as described above with respect tomotors 10 in FIG. 4. Likewise, if one channel of the machine 10′ shouldfail in a short circuit, open circuit or ground (whether in the motor10′ itself, or in the drive electronics or lead wires), the drive to theremaining channel, is adjusted to compensate for the loss in torque, andthe failed channel is no longer driven. The drive of the failed channelis effectively disconnected by bringing current flow in the windings tozero, resulting in the impedance of the main phase windings of thechannel increasing to a high value, as previously described, such thatthe drag torque due to a short circuit type failure in the channel, isminimized. This multi-channel configuration offers two fully redundantsystems (i.e. channel A and channel B) with a minimum, of hardware,thereby minimizing weight and space and increasing reliability- Channelfailure detection may be achieved using any suitable approach, such asincorrect speed or torque as a function of current, voltage, hightemperature, machine impedance, etc.

Referring again to FIG. 6, the stator of the multi-channel motor 10′preferably includes means for impeding cross-talk between the tertiarymagnetic circuits of channels A and B, such as is described inapplicant's co-pending application Ser. No. 11/419,238 filed May 19,2006. As described in that application, the presence of a cross-talkreduction feature, such a stator slit 21 acts to substantially contain,the tertiary magnetic within the channel. As such, the tertiary magneticpreferably travels along the entire length of the control flux bus 32 tothe channel boundary, where the presence of the cross-talk reductionslit 21 redirects the flux up to power flux bus 36, where it thentravels back alexia entire length of the power flux bus 36 (this flux isnot present, and therefore not depicted, in the single channelembodiment of FIG. 2), until the path joins up again with the beginningof the tertiary path, in the vicinity of another cross-talk reductionslit 21.

Referring to FIG. 7, a control system for dual-channel motor 10′ isshown. FIG. 7 is similar to FIG. 4, but for the configuration of motor10′ in FIG. 7 relative to two motors 10 of FIG. 4. Motor drives 68A and68B are preferably each as described above with respect to FIG. 5, andthis two independent motor drives are provided, one for each channel ofmotor 10′. In use, a similar operation is obtained when the controlscheme of FIG. 5 is applied to the dual channel motor 10′ of FIG. 7.Accordingly, in normal operation, channels A and. B may be operatedseparately, or conjunctively, and motor drives 68A and 68B arecontrolled accordingly by controller 69. When, a failure is detected onone motor channel, the current flow in its respective control windings24 is set to zero in order to increase impedance of the phase windingsand thereby minimise a drag torque and other undesirable effectsotherwise brought on by the failed channel.

The dual-channel design of FIGS. 6 and 7 offers obvious size and weightsavings over the two motors system as shown in FIGS. 4 and 5. The twomotor design of FIG. 4 and 5, however, has its own advantages over thedual-channel arrangement of FIGS. 6 and 7, such as simplicity ofindividual components.

The skilled reader will appreciate that a failure is not required toturn a channel or motor “off” as described above, but rather theapproach may be used in any suitable situation where it is desired toshut a channel “off”, including as part of a normal operation scheme.

In another control scheme, depicted in FIG. 7, the dual motorarrangement of FIG. 4, or as the case may be, the dual, channel motor ofFIG. 7, is controlled using a modified motor drive 68′ in which buckregulator 72 has a dedicated filter inductor 83 independent from thecontrol windings 24. Separate DC current sources 80 and 81 respectivelydrive the phase and control windings independently from one another.Phase windings may be driven as described above with respect to FIGS. 5and 7, so that torque is split as desired among the motors or channelsin normal operation, during which time the DC source 81 provides controlcurrent at a sufficient level to keep the control flux bus fullysaturated at all times, for reasons already described. In the event of achannel failure, phase winding current in the other motor/channel isadjusted to compensate for the loss of torque due to the failed channel,while the current from source 81 to the control winding(s) for thefailed channel is brought to zero to minimize the drag torque due to thefailed channel,

In this embodiment, the control winding has different design constraintsthan the above embodiments, and thus the control winding may have ahigher number of turns relative to the phase windings, to minimise theamount of control current required to saturate and maintain saturationin under the influence of desaturating fluxes from the main phases.

In the arrangement of FIG. 7, where the control current is supplied froma source separate from the phase windings, and is independently variablerelative to the phase windings, if the phase winding current in themotor/channel exceeds a specific value, such as a desired maximum limit,the inductance of the phase winding will abruptly increase, tending tolimit the current in the phase winding to that specific value or limit.This can be used to simplify the drive system, of very low impedance(i.e. high speed) PM motors. For example, the motor can be designedusing this feature to intrinsically limit inrush current on start-up byappropriately designing this feature into the motor, such that othertypical inrush limiting techniques, such as duty cycle control, may beomitted or operated at lower frequencies.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without department from the scope of the invention disclosed.For example, the number of phases in the motors could be varied andcould be to any number. The motors may be single or multi-phase, singleor multi-channel. The windings may have single or multiple turns perslot, the number of turns of a winding not; necessarily has to be awhole number. The number of phase windings does not necessarily have toequal the number of control windings, and one or more windings mayperhaps be present in a slot. The windings may be any conductor(s) (i.e.single conductor, more than one wire, insulated, laminated, hits etc) ormay be superconductors. In multiphase alternators, there may be delta orY-connected windings in accordance with suitable techniques. There neednot be an air gap between the phase and control windings, as long as thewindings are electrically isolated from one another. The rotor can beany electromagnetic configuration suitable (i.e. permanent magnet rotornot necessary), and may be provided in an outside or insideconfiguration, or any other suitable configuration. Other windingconfigurations are possible, and those described above need not be usedat all, or throughout the apparatus. Also, the magnetic circuitsdescribed can be arranged in the stator (and/or rotor) in any suitablemanner. The magentic circuits need not be provided in the same stator,but rather the primary and secondary magnetic circuits may be providedin separate stator elements. Any suitable stator configuration may beused, and the stator of FIGS. 1 and 4 are exemplary only. The statorneed not be slotted as shown, nor slotted at all. The arrangement of theprimary, secondary and tertiary magnetic circuits, and the arrangementof phase winding saturation apparatus(s) in the motors may be anysuitable arrangement. Likewise, the stator and rotor may also have anysuitable configuration. Although DC is preferred in the control windings24 of the motor or channel, any suitable saturating arrangement may beused. For example, a suitable saturation apparatus may be provided usingpermanent magnetic means to selectively saturate a portion of thesecondary magnetic circuit, rather than using the electromagnetic meansof the control winding. Any suitable motor drive arrangement may beemployed. The present technique may also be employed with stand-alonemotors if desired, and redundant systems are not required, but merelyone apparatus arrangement: which may benefit from the application of theabove principles. Still other modifications which fall, within the scopeof the present invention will be apparent to those skilled in the art,in light of a review of this disclosure, and such modifications areintended to fail within the appended claims.

1. An electric motor system comprising a motor having a magnetic rotorand a magnetically conductive stator, the stator having at least twowindings connected with one another in series, the rotor and statortogether defining at least a first magnetic circuit encircling a firstportion of a first one of the stator windings, the stator defining atleast a second magnetic circuit therein, a second one of the statorwindings wrapped around a portion of the stator remote from the firstmagnetic circuit, the second stator winding and said portion of thestator thereby providing an inductor assembly, the second magneticcircuit passing through said stator portion and encircling a secondportion of the first stator winding and a portion of the second statorwinding, the second magnetic circuit remote from the first magneticcircuit and remote from the rotor, the motor system having a buckregulation apparatus connected in series between a direct current (DC)electricity source and the second winding, wherein the inductor assemblyprovides a filter inductor function for the buck regulator.
 2. Theelectric motor system as defined in claim 1, further comprising acommutation apparatus connected in series between the second and firstwindings and adapted to commutate DC electricity provided by the secondwinding into alternating current (AC) electricity to be provided to thefirst winding.
 3. The electric motor system as defined in claim 1,wherein a plurality of first windings are provided in a three-phaseconfiguration.
 4. The electric motor system as defined in claim 1,wherein second winding is wound in sufficient turns around said statorportion such that electricity passing through the second winding fromthe direct current source saturates said stator portion.
 5. The electricmotor system as defined in claim 1, further comprising a failuredetection apparatus communicating with the DC source for interruption ofan electricity supply of the DC source to the motor upon detection of afault in the motor system requiring motor shutdown.
 6. The electricmotor system as defined in claim 1, further comprising at least a secondmotor system as defined in claim 1, and wherein the at least two motorsystems are co-mounted on a common shaft.
 7. The electric motor systemas defined in claim 6, wherein the at least two motor systems have acommon rotor and stator, and wherein the at least two motor systems areseparately controllable, and wherein the windings of the respectivemotor systems are confined to distinct non-overlapping sectors of thecommon stator.
 8. A method for controlling an electric motor system, thesystem including at least one motor having a magnetic rotor and amagnetically conductive stator having at least one winding, the rotorand stator together defining at least a first magnetic circuitencircling a first portion of a first one of the stator windings, thestator defining at least a second magnetic circuit therein, the secondmagnetic circuit encircling a second portion of the first statorwinding, the second magnetic circuit remote from the first magneticcircuit and remote from the rotor, the method comprising the steps of:operating the motor to drive an output shaft thereof, the step ofoperating including the step of saturating at least a portion of thesecond magnetic circuit to maintain an impedance of said winding at afirst value during operation; requiring motor shutdown; and thenshutting down the motor, including the step of de-saturating at leastsaid portion of the second magnetic circuit to increase the impedance ofthe winding to a second value, the second value significantly higherthan the first value such that current flow in the winding iseffectively limited to a desired value.
 9. The method of claim 8 whereinthe desired current value is substantially zero, such that drag torquegenerated by continued rotation of the motor is substantially zero. 10.The method of claim 8 further comprising the step of continuing to drivethe output shaft after said step of shutting down the motor.
 11. Themethod of claim 10 wherein the output shaft is driven by at least asecond motor connected to the shaft.
 12. The method of claim 11, furthercomprising the step of adjusting an output torque of the second motorafter the step of shutting down, to compensate to the lost torqueattributed to said step of shutting down the other motor.
 13. The methodof claim 8 wherein the step of requiring motor shutdown includes thestep of detecting a fault in the motor.
 14. The method of claim 8wherein the step of saturating at least a portion of the second magneticcircuit includes passing a saturating current through a second windingwrapped around a portion of the stator remote from the first magneticcircuit carrying said portion of the second magnetic circuit, andwherein the step of de- saturating at least said portion of the secondmagnetic circuit includes reducing a current level in said secondwinding below a saturation current level.